Low-temperature membrane separation device and method for capturing carbon dioxide at high concentration

A membrane separation method for capturing carbon dioxide, in which a gas mixture is passed through a membrane unit to selectively separate the carbon dioxide, the membrane unit having a feed side, into which a carbon-dioxide-containing gas is provided, a retentate side, from which a carbon-dioxide-depleted stream is discharged, and a permeate side, from which a carbon-dioxide-enriched stream is produced, the membrane separation method comprising:

• a first separation step of passing the gas mixture through a first membrane unit, which is connected at a feed side thereof to a first feed gas line;
• a second separation step of passing the carbon-dioxide-enriched stream, withdrawn from the permeate side of the first membrane unit, through a second membrane unit, which is connected at a feed side thereof to a second feed gas line;
• and
• a step of cooling a feed gas of the second membrane unit through a feed-gas-cooling device, between the first separation step and the second separation step,
• wherein the second separation step is performed at a temperature that is lower than a temperature at which the first separation step is performed,
• wherein the temperature at which the first separation step is performed is determined by adjusting at least one of a temperature of the first membrane unit and a temperature of the gas mixture provided into the first membrane unit, and the temperature at which the second separation step is performed is determined by adjusting at least one of a temperature of the second membrane unit and a temperature of the gas which permeates the first membrane unit and is then provided into the second membrane unit,
• wherein the feed-gas-cooling device includes a coil unit which is extended to the second feed gas line.